The invention relates to an elevator installation comprising at least one car, which can be made to travel in a shaft along a traveling path and has a safety gear, wherein a control unit, a drive and a brake are associated with the car, and further comprising a safety device with a speed determining unit for determining the current speed of the at least one car, a distance determining unit for determining the actual distance of the at least one car from an obstacle, another car or an end of the shaft, and a determining unit for determining a critical distance and a minimum distance, which are dependent on the speed of the at least one car, it being possible by means of the safety device to trigger an emergency stop of the at least one car if the actual distance is less than the critical distance, and it being possible to trigger the safety gear of the at least one car if the actual distance is less than the minimum distance, wherein the movement of the car when an emergency stop is properly performed follows an emergency stop traveling curve, which represents the variation in speed of the car that is to be expected when the emergency stop is triggered, in dependence on the distance covered by the car, and wherein the movement of the car when the safety gear is functioning properly follows a safety gear traveling curve, which represents the variation in speed of the car that is to be expected when the safety gear is triggered, in dependence on the distance covered by the car.
Elevator installations of this type are known from WO 2004/043842 A1. They can be used to transport persons and/or loads in an effective way, in that the at least one car is made to travel up or down within the shaft along the traveling path. To avoid the car colliding with an obstacle, another car or an end of the shaft, the elevator installation has a safety device with a speed determining unit and a distance determining unit, with the aid of which the current speed of the car and the distance of the car from an obstacle, another car or an end of the shaft can be determined. The safety device also has a determining unit by means of which a critical distance, dependent on the speed of the car, can be determined. If the determined distance goes below the critical distance, an emergency stop of the at least one car can be triggered by the safety device. When an emergency stop is performed, the brake associated with the car is activated and, at the same time, its drive motor is deactivated, so that the car can be brought to a standstill with considerable braking acceleration (deceleration) within a short time. In the event of a fault, for example of the brake, to avoid a collision the safety device has a further safety stage, in that the safety gear can be triggered in time before a collision. For this purpose, a minimum distance, dependent on the speed of the at least one car, can be determined by the determining unit. If the actual distance determined by the distance determining unit goes below the minimum distance, the safety gear of the car is activated, so that the latter is brought to a standstill with very high braking acceleration (deceleration) within a very short time. The minimum distance is less than the critical distance, but it is in any event set such that it provides the braking distance that occurs when the safety gear is triggered without a car collision occurring.
When an emergency stop is properly performed, the movement of the car follows an emergency stop traveling curve. This is obtained from the current speed of the car and the braking acceleration (deceleration) occurring when an emergency stop is performed. It represents the variation in speed that is to be expected when the emergency stop is triggered, in dependence on the distance covered by the car.
If the safety gear is triggered, the movement of the car when the safety gear is functioning properly follows a safety gear traveling curve. This is obtained from the current speed of the car and the braking acceleration (deceleration) occurring when the safety gear is active. It represents the variation in speed that is to be expected when the safety gear is triggered, in dependence on the distance covered by the car.
In WO 2004/043842 A1, it is proposed to determine both the critical distance and the minimum distance in dependence on the speed of the car. This provides the possibility of shortening the critical distance and also the minimum distance when the car has a low speed, since in this case only a relatively short braking distance is required for braking the car. If, on the other hand, the car has a relatively high speed, allowance must be made for long braking distances and, accordingly, both the critical distance and the minimum distance must be chosen to be greater.
The fact that first an emergency stop and, if it malfunctions, the safety gear can be triggered one after the other to avoid a car collision means that the collision of a car can be reliably prevented. To make sure that the car can be brought to a standstill by means of the safety gear in the event of a malfunction of the emergency stop, usually a large value is used for the critical distance, even at low car speeds. This has the advantage that, after triggering an emergency stop, it can first be checked whether the movement of the car follows the emergency stop traveling curve to the speed of zero. If this is not the case, the safety gear can still be triggered to bring the car to a standstill after running through the safety gear traveling curve. However, this entails the disadvantage that, in normal operation, the at least one car must be at a considerable distance from an obstacle, another car or an end of the shaft even at low speeds. In particular when using a number of cars which can be made to travel independently of one another along a common traveling path, it may have the consequence that two cars cannot simultaneously travel to two floors that are directly one above the other, since the distance between the floors is in many cases smaller than the distance between the cars that is to be maintained to avoid the triggering of an emergency stop or the safety gears.
It is an object of the invention to develop an elevator installation of the type mentioned at the beginning in such a way that the distance that is to be maintained by the at least one car from an obstacle, another car or an end of the shaft can be reduced without an emergency stop or a safety gear being triggered, but a car collision can be reliably prevented.